Direction-specific release induced through osmotic pressure inside giant microcapsules is realized and monitored at high and low concentrations of encapsulated polymer. A clear correlation between the release kinetics upon opening the shell and encapsulated polymer concentration is observed. This has been independently confirmed by shell opening via nanoindentation and laser radiation. To quantify these observations, the internal pressure of the capsules is determined by analysis of mechanical tests performed via colloidal probe AFM. As expected, larger amounts of encapsulated material lead to increased internal pressures and enhanced release kinetics. The results show how drug release can be accelerated by encapsulation of osmotic pressure generating species. Such pressurized capsules systems show large ejection velocities and are envisioned as an inexpensive biolistic transfection device for in vitro applications.